1. Field of the Invention
The present invention relates to a pixel circuit which has a current driving type light-emitting device such as an organic electroluminescent device (hereinafter, called xe2x80x9corganic EL devicexe2x80x9d) and a driving device such as a thin film transistor for driving the current driving type light-emitting device. The present invention also relates to a display apparatus having pixels, each pixel being provided with such a pixel circuit, and further to an electronic apparatus having the same. In particular, the present invention concerns a driving circuit, as well as a display apparatus, capable of compensating for deterioration with time of the current driving type light-emitting device and the driving device, as well as to an electronic device incorporating such a driving circuit and a display apparatus.
2. Description of Related Art
As an example of such a display apparatus, a display apparatus of the type using a Thin Film Transistor (hereinafter abbreviated as a TFT) for driving a current driving type light-emitting device such as an organic EL device as a driving device is configured as will be described. That is, a data signal and a scanning signal, each corresponding to an image to be displayed, are respectively supplied to a signal line and a scanning line provided in a display region from a scanning line driving circuit and a signal line driving circuit. On the other hand, a voltage is applied between a pixel electrode and an opposing electrode at each pixel through a driving TFT provided for each of a plurality of matrix pixels in a display region from a common electrode driving circuit and an opposing electrode driving circuit. Then, a current flowing through a current driving type light-emitting device arranged between the pixel electrode and the opposing electrode is controlled by the TFT for driving each pixel in accordance with a data signal voltage supplied from the signal line at the same time as a scanning signal is supplied from the scanning line.
More specifically, for example, a switching TFT is provided for each pixel for supplying a data signal from the signal line to a gate of the driving TFT through a source and a drain when a scanning signal is supplied from the scanning line to the gate. The conductance between the source and the drain of the driving TFT is controlled (changed) according to a voltage (i.e., a gate voltage) of a data signal supplied to the gate. At this time, the gate voltage is retained for a longer time than the period that the data signal is supplied by a retention capacitor connected to the gate. In addition, a driving current is supplied to an organic EL device, etc. through the source and the drain whose conductance is thus controlled, thereby driving the organic EL device in accordance with a driving current.
Especially, the organic EL device equipped with the driving TFT described above is considered promising as a current control type light-emitting device (hereinafter, described as xe2x80x9cTFT-OELDxe2x80x9d) for realizing a display panel featuring a large size, highly resolution, a wide viewing angle, and low power consumption.
However, for a current driving type light-emitting device such as an organic EL device, a driving current flows through the inside of the device, so that deterioration over time occurs irrespective of scale. For example, with respect to the organic EL device, it has been reported that significant deterioration over time occurs. (Refer to Jpn. J. Appl. Phys., 34, L824 (1995)). The deterioration of the organic EL device over time is broadly classified into two types. One of them is a reduction in current against a voltage applied to the organic EL device. The other is a reduction in a quantity of emitted light against a given voltage applied to the organic EL device or a current flowing therethrough. Additionally, the degree of deterioration over time varies among each organic EL device. Further, for a TFT-OELD, the TFT deteriorates over time because of a current flowing through the TFT as a driving device. For this reason, in a display apparatus employing the TFT-OELD, a problem of deterioration in image quality arises when the organic EL device or the driving TFT deteriorates over time. That is, deterioration in current decrease or a quantity of emitted light decrease leads to degradation of screen luminance, while variation in these decreases cause screen irregularities. Especially, these kinds of deterioration occur depending upon luminescence characteristics of the organic EL device during manufacture, variations in current-voltage characteristics or threshold characteristics of the driving TFT or history of display patterns, and so forth, thus resulting in deterioration in screen quality of an entire display apparatus, and screen irregularities.
In this connection, Japanese Patent Publication No. 05-019234 discloses a conventional art that an EL device is used as a rear light source (backlight) of a liquid crystal display panel to thereby detect the luminance of the EL device in such a manner that the luminance of an entire liquid crystal display panel lightened from the rear by the EL device does not decrease, thereby correcting for deterioration of the rear light source. However, the conventional art relates to an entire liquid crystal display panel, and an EL device is not provided for each pixel as a display device, and is used merely as a rear light source. Therefore, the conventional art substantially differs from the present invention in its applicability. Additionally, the conventional art does not suggest an effective technology for correcting deterioration over time described above in a display apparatus having each pixel equipped with a current driving type light-emitting device such as an organic EL device. Furthermore, the technical problems of increasing the longevity of a display apparatus or improving the display quality by correcting for deterioration over time in a driving TFT or a current driving type light-emitting device in a display apparatus equipped with a current driving light-emitting device at each pixel is not recognized between and by those skilled in the art.
In view of the above-described problems, to solve the technical problems described above, it is an object of the present invention to provide a pixel circuit, a display apparatus and an electronic apparatus equipped with a current driving type light-emitting device which is capable of reducing degradation of screen luminance or screen irregularities by appropriately correcting for deterioration over time when deterioration over time causes a reduced current or a reduced quantity of emitted light or dispersion of deterioration over time in a current driving light-emitting device.
(1) To solve the problems described above, the present invention provides a first display apparatus comprising: a current driving type light-emitting device provided for each pixel; a driving device provided for each the pixel, for controlling a driving current flowing to the light-emitting device according to a voltage of a data signal; a power source unit for supplying power source voltage through a power wire to cause the driving current to flow through the light-emitting device via the driving device; a signal wire driving unit for supplying the data signal to the driving device through a signal wire; and a voltage adjusting unit for adjusting at least one of the power source voltage of the power source unit and the data signal at the signal wire driving unit, in such a manner that, when a data signal of a predetermined voltage is supplied to the driving device through the signal wire, at least one of a quantity of driving current flowing and a quantity of light emitted by the light-emitting device approaches a predetermined reference value.
In the first display apparatus as defined above, a driving current flows to the light-emitting device via the driving device, as the power source voltage is supplied from the power source unit, while the driving device is supplied with a data signal from the signal wire driving unit via a signal wire. The driving current flowing through the light-emitting device is controlled by the driving device in accordance with a voltage of the data signal. As a consequence, the current driving type light-emitting device emits light by the driving current, in accordance with a voltage of the data signal. When a data signal of a predetermined voltage is supplied to the driving device through the signal line in, for example, a non-display period, the voltage adjusting unit serves to control at least one of the power source voltage at the power source unit and the voltage of the data signal at the signal wire driving unit, in such a manner that a quantity of driving current flowing through the light-emitting device or a quantity of light emitted from the light-emitting device approaches a predetermined reference value( i.e., a reference current or a reference light quantity).
Hence, even if a light-emitting device or a driving current is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes increase in a resistance of the light-emitting device or the driving device, a quantity of driving current or a quantity of light emitted in the corresponding light-emitting device is maintained substantially constant. Thus, any decrease in the quantity of driving current or the quantity of emitted light, attributable to deterioration over time of the light-emitting device or the driving device, can be appropriately compensated for by carrying out voltage adjustment.
Further, even if there are variations in current-voltage characteristics or current-light emitting characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current or the quantity of emitted light in the light-emitting device of the corresponding plurality of pixels can be substantially equalized, if the voltage control by the voltage adjusting unit is performed on independent pixels. That is to say, variations of a quantity of driving current and a quantity of emitted light, attributable to the variations in the characteristics of the light-emitting device or the driving device, can effectively be corrected.
Thus, according to the first display apparatus, in a display apparatus in which the current driving type light-emitting device such as an organic EL device is driven by the driving device such as a thin film transistor, a decrease in screen luminance and screen irregularities caused by deterioration over time or variations in characteristics in each device can be reduced.
(2) In one form of the first display apparatus, the driving device comprises a thin film transistor having a gate to which the data signal is supplied, and a source and a drain between which the driving current flows, a conductance between the source and the drain being controlled by a gate voltage.
In this form of this display apparatus, the conductance between the source and the drain is controlled (changed) in accordance with the data signal supplied to the gate of the thin film transistor. It is therefore possible to control the driving current flowing through the source and the drain to the light-emitting device, in accordance with the voltage of the data signal.
(3) In another form of the first display apparatus, the voltage adjusting unit comprises: a current measuring unit for measuring a quantity of driving current when a data signal of the predetermined voltage is supplied to the driving device; and a voltage control unit for adjusting at least one of the voltages such that the measured current approaches a predetermined reference current.
In this form of this display apparatus, a quantity of driving current is measured by the current measuring unit when the data signal of a predetermined voltage is supplied to the driving device. Additionally, the voltage of the data signal or the power source voltage of the driving current is adjusted by the voltage controlling unit in such a manner that the current thus measured comes close to a predetermined reference current.
Thus, even if a driving current is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes an increase in a resistance of the light-emitting device or the driving device, a quantity of driving current in the corresponding light-emitting device is maintained substantially constant. Further, even if there are variations in current-voltage characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current in the light-emitting device of the corresponding plurality of pixels can be maintained substantially constant, if the voltage control of the data signal by the voltage adjusting unit is performed on independent pixels.
(4) In still another form of the first display apparatus, the voltage adjusting unit comprises: a light-emitting measuring unit for measuring the quantity of the emitted light at the time when a data signal of the predetermined voltage is supplied to the driving device; and a voltage control unit for adjusting at least one of the voltages such that the measured quantity of emitted light approaches the reference quantity of emitted light.
According to this form of this display apparatus, a quantity of light emitted from the light-emitting device obtained by supplying a data signal of a predetermined voltage to the driving device is measured by a emitted light quantity measuring unit. A voltage of the data signal or power source voltage for driving current is controlled by the voltage controlling unit in such a manner that the measured light quantity comes close to the predetermined reference light quantity.
Thus, even if a light-emitting device is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes an increase in a resistance of the light-emitting device or the driving device, a quantity of light emitted from the light-emitting device is maintained substantially constant. Further, even if there are variations in current-voltage characteristics or current-light emitting characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current in the light-emitting device of the corresponding plurality of pixels can be maintained substantially constant, if the voltage control of the data signal by the voltage adjusting unit is performed on independent pixels.
(5) In a further form of the first display apparatus, a controller is further provided for controlling the voltage adjusting unit so as to adjust at least one of the voltages at a non-display period prior to a display period.
In this form of this apparatus, the voltage of data signal or power source voltage for the driving current is controlled by the voltage adjusting unit under the control of a controller at a non-display period preceding a display period. As a result, it is not necessary to occupy part of the display period for the purpose of measurement. In addition, the voltage control operation is carried out by the voltage adjusting unit, without affecting the screen display at a display period. Additionally, often it is enough to carry out the adjusting operation by the voltage adjusting unit at each non-display period such as at power-up.
(6) To solve the technical problems described above, a second display apparatus in accordance with the present invention comprises: a current driving type display light-emitting device provided for each pixel of a display region; a driving device provided for each the pixel, for controlling a driving current flowing to the display light-emitting device according to a voltage of a data signal; a power source unit for supplying a power source voltage through a power wire to cause the driving current to flow to the display light-emitting device via the driving device; a signal wire driving unit for supplying the data signal to the driving device through a signal wire; a current driving type monitoring light-emitting device provided in a monitoring region and driven by current in the same manner as the display light-emitting device; and a voltage adjusting unit for adjusting at least one of the power supply of the power source unit and the data signal at the signal wire driving unit, in such a manner that at least one of a quantity of driving current flowing and a quantity of light emitted by the monitoring light-emitting device comes close to a predetermined reference value.
In the second display apparatus as defined above, a driving current flows to the display light-emitting device via the driving device, as the power source voltage is supplied from the power source unit, while the driving device is supplied with a data signal from the signal wire driving unit through the signal wire. The driving current flowing through the display light-emitting device is controlled by the driving device in accordance with a voltage of the data signal. As a consequence, the current driving type display light-emitting device emits light by the driving current, in accordance with the voltage of the data signal. When a data signal of a predetermined voltage is supplied to the driving device through the signal wire in, for example, a non-display period, the voltage adjusting unit serves to control at least one of the power source voltage of the power source unit and the voltage of the data signal at the signal wire driving unit, in such a manner that a quantity of driving current flowing through the current driving type monitoring light-emitting device, which is driven by current as in the case of the display light-emitting device, or a quantity of light emitted from the current driving type monitoring light-emitting device approaches a predetermined reference value( i.e., a reference current or a reference light quantity).
The monitoring light-emitting device which is provided in the monitoring region is driven by current as in the case of the display light-emitting device provided in the display region. It is therefore expected that the monitoring light-emitting device exhibits a tendency of deterioration over time similar to that exhibited by the display light-emitting device.
Hence, even if a driving current and a display light-emitting device are impeded as a result of deterioration over time of the display light-emitting device or the driving device which causes increase in a resistance of the display light-emitting device or the driving device, a quantity of driving current or a quantity of light emitted in the corresponding monitoring light-emitting device is maintained substantially constant. Thus, any decrease in a quantity of driving current or a quantity of emitted light, attributable to deterioration over time of the display light-emitting device or the driving device, can be appropriately compensated for by carrying out the voltage adjustment.
Further, even if there are variations in current-voltage characteristics or current-light emitting characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current or the quantity of emitted light in the light-emitting device of the corresponding plurality of pixels can be substantially equalized, if the voltage control by the voltage adjusting unit is effected on independent pixels. That is to say, variations of the driving current and emitted light quantity, attributable to the variations in the characteristics of the light-emitting device or the driving device, can effectively be corrected.
Thus, according to the second display apparatus, in a display apparatus in which the current driving type light-emitting device such as an organic EL device is driven by the driving device such as a thin film transistor, a decrease in screen luminance and screen irregularities at each pixel caused by deterioration over time can be reduced.
(7) In one form of the second display apparatus, the driving device comprises a thin film transistor having a gate to which the data signal is supplied, and a source and a drain between which the driving current flows, a conductance between the source and the drain being controlled by a gate voltage.
In this form of this display apparatus, when a data signal is supplied to the gate of the thin film transistor, the conductance between its source and drain is controlled (changed) by a gate voltage. Accordingly, the driving current flowing through the display light-emitting device via its drain and source can be controlled in accordance with the voltage of the data signal.
(8) In another form of the second display apparatus, the voltage adjusting unit comprises: a current measuring unit for measuring a quantity of current in the monitoring light-emitting device; and a voltage control unit for adjusting at least one of the voltages such that the measured current approaches a predetermined reference current value.
According to this form of the display apparatus, a current in the monitoring light-emitting device is measured by the current measuring unit. A voltage of the data signal or a power source voltage of the driving current is controlled by the voltage control unit such that the measured current approaches a predetermined reference current.
Accordingly, even if a driving current is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes an increase in a resistance of the light-emitting device and the driving device, a quantity of driving current in the corresponding light-emitting device is maintained substantially constant. Further, even if there are variations in current-voltage characteristics in the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current in the light-emitting device of the corresponding plurality of pixels can be substantially equalized, if the voltage control is performed on independent pixels.
(9) According to a further form of the second display apparatus, the voltage adjusting unit comprises: a light-emitting measuring unit for measuring a quantity of light emitted from the monitoring light-emitting device; and a voltage control unit for adjusting at least one of the voltages such that the measured quantity of emitted light approaches the reference quantity of emitted light.
According to this form, the quantity of light emitted from the monitoring light-emitting device is measured by the light measuring unit, and the voltage of the data signal or the power source voltage for the driving current is controlled by the voltage control unit, in such a manner that the measured light quantity approaches a predetermined reference light quantity.
Accordingly, even if a light-emitting device is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes an increase in a resistance of the light-emitting device and the driving device, a quantity of light emitted in the corresponding light-emitting device is maintained substantially constant. Further, even if there are variations in current-voltage characteristics or current-light-emitting characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current in the light-emitting device of the corresponding plurality of pixels can be substantially equalized, if the voltage control of the data signal by the voltage adjusting unit is performed on independent pixels.
(10) A further form of the second display apparatus further comprises: a controller for controlling the voltage adjusting unit so as to adjust at least one of the voltages at a non-display period preceding a display period.
According to this form of this display apparatus, the voltage control unit controls the voltage of the data signal or the power source voltage for the driving current, under the control of a controller, in a non-display period preceding a display period. Therefore, the voltage control operation by the voltage adjusting unit can be performed without affecting the image display which is displayed in the display period.
(11) In a further form of the second display apparatus, the display light-emitting device and the monitoring light-emitting device are formed on a common substrate.
According to this form of this display apparatus, it is possible to expect similar tendency of deterioration over time both on the display light-emitting device and the monitoring light-emitting device, by operating these light-emitting devices under the same or similar conditions. This enables a highly accurate control of voltage adjustment on the display light emitting device, based on the current or light quantity on the monitoring light-emitting device.
(12) In a still further form of the second display apparatus, the display light-emitting device and the monitoring light-emitting device are formed in an identical step of process.
This form of the display apparatus offers an advantage in that the production process does not necessitate any additional step which otherwise may be required for forming the monitoring light-emitting device. Further, it is rather easy to form the display light-emitting device and the monitoring light-emitting device with the same or similar characteristics and, hence, with the same or similar tendencies of deterioration over time.
(13) In a yet further form of the second display apparatus, the power source voltage unit provides a power source which supplies the driving current during a display period both to the display light-emitting device and the monitoring light-emitting device.
With this form, the display light-emitting device and the monitoring light-emitting device exhibit similar or the same tendencies of deterioration over time, since both these light-emitting devices are supplied with driving current during the display periods.
(14) To solve the technical problems described above, the present invention provides a pixel circuit provided for each of a plurality of matrix pixels constituting a display region of a display apparatus having, at least, a signal wire to be supplied with a data signal and first and second feeder lines for supplying power source voltage to flow a driving current, the pixel circuit comprising: a current driving type light-emitting device connected between the first and second feeder lines; a first thin film transistor (current-controlling thin film transistor) controlling the driving current flowing through the light-emitting device via a source and a drain connected between the first and second feeder lines in series to said light-emitting device in accordance with a voltage of said data signal supplied to a gate; and a driving current compensation device for increasing the driving current according to at least one of a decrease in a quantity of driving current and a decrease in a quantity of light emitted from the light-emitting device.
According to the pixel circuit of the present invention, supplying power source via first and second feeder lines causes a driving current to flow to the light-emitting device via the source and the drain of the first thin film transistor. Meanwhile, a data signal is supplied to a gate of the first thin film transistor via the signal wire. In the meantime, a conductance between the source and the drain of the first thin film transistor is controlled (changed) by a gate voltage, so that the driving current flowing to the light-emitting device is controlled according to the voltage of the data signal. As a result, the current driving type light-emitting device illuminates in accordance with the voltage of the data signal. Additionally, the driving current flowing as described above is increased by the driving current compensation device in accordance with a decrease in quantity of driving current or quantity of light emitted.
Hence, even if the driving current or the light-emitting device is impeded as a result of deterioration over time of the light-emitting device or the first thin film transistor which causes an increase in a resistance of the light-emitting device or the first thin film transistor, a quantity of driving current or a quantity of emitted light in the light-emitting device is maintained substantially constant.
That is, any decrease in the quantity of driving current or the quantity of emitted light caused by deterioration over time of the light-emitting device or the first thin film transistor can automatically be corrected by an operation to increase the driving current through, for example, a reduction in a resistance effected by the driving current compensation device.
Further, since the correction described above is made separately for each of a plurality of pixels, even if there are variations in current-voltage characteristics and current-light-emitting characteristics of the light-emitting device or the first thin film transistor among a plurality of pixels, a quantity of driving current or a quantity of emitted light in the corresponding light-emitting device can be maintained substantially constant. That is, any variation in the quantity of driving current or the quantity of emitted light caused by variation of characteristics of the light-emitting device or the first thin film transistor can be automatically corrected.
As a result, according to the pixel circuit of the present invention, in a pixel circuit in which a current driving type light-emitting device such as an organic EL device is driven by a first thin film transistor, a decrease in screen luminance or screen irregularities caused by deterioration over time or variations in characteristics in each device can be reduced.
(15) In one embodiment of the pixel circuit, the signal wire includes a signal line to be supplied with the data signal and a scanning line to be supplied with a scanning signal. In addition, the pixel circuit further comprises a second thin film transistor (switching thin film transistor) connected in such a manner that the data signal is supplied to a gate of the first thin film transistor via a drain and a source when the scanning signal is supplied to a gate. According to this embodiment, supplying a scanning signal to the gate of the second thin film transistor via a scanning line causes the source and drain of the second thin film transistor to be brought into conduction. In parallel therewith, supplying a data signal to the source or the drain of the second thin film transistor via the signal line causes the data signal to be supplied to the gate of the first thin film transistor via the source and the drain of the second thin film transistor.
(16) In another embodiment of the pixel circuit, the driving current compensation device controls a resistance between the first feeder line and the second feeder line depending upon a relation between a voltage across the light-emitting device and a quantity of the driving current.
According to this embodiment, by adjusting a resistance between the first feeder line and the second feeder line by the driving current compensation device depending upon a relationship between a voltage across the light-emitting device and a quantity of driving current, the driving current is increased to compensate for a reduction of the same driving current.
(17) In the pixel circuit in which the control is performed depending upon the relationship between a voltage and a current, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the driving current compensation device includes a first correction thin film transistor of an n-channel type having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the light-emitting device and the second feeder line in series to the light-emitting device.
In this case, a resistance between the first feeder line and the second feeder line is adjusted by the first correction thin film transistor of an n-channel type, so that the driving current is increased to compensate for a reduction of the same driving current.
(18) Alternatively, in the pixel circuit in which the control is performed depending upon the relationship between a voltage and a current, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the driving current compensation device includes a first correction thin film transistor of a p-channel type having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the light-emitting device and the second feeder line in series to the light-emitting device.
In this case, a resistance between the first feeder line and the second feeder line is adjusted by the first correction thin film transistor of a p-channel type, so that the driving current is increased to compensate for a reduction of the same driving current.
(19) Alternatively, in the pixel circuit in which the control is performed depending upon the relationship between a voltage and a current, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the driving current compensation device includes a second correction thin film transistor of a p-channel type having a gate connected to an electrode on the second feeder line side of the light-emitting device and a source and a drain connected between the light-emitting device and the second feeder line in series to the light-emitting device.
In this case, a resistance between the first feeder line and the second feeder line is adjusted by the second correction thin film transistor of a p-channel type, so that the driving current is increased to compensate for a reduction of the same driving current.
(20) Alternatively, in the pixel circuit in which the control is performed depending upon the relationship between a voltage and a current, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the driving current compensation device includes a second correction thin film transistor of an n-channel type having a gate connected to an electrode on the second feeder line side of the light-emitting device and a source and a drain connected between the light-emitting device and the first feeder line in series to the light-emitting device.
In this case, a resistance between the first feeder line and the second feeder line is adjusted by the second correction thin film transistor of an n-channel type, so that the driving current is increased to compensate for a reduction of the same driving current.
(21) In a different embodiment of the pixel circuit, a retention capacitor is further provided which is connected to a gate of said first thin film transistor, for retaining a gate voltage of the first thin film transistor.
According to this embodiment, the gate voltage of the first thin film transistor, after being supplied with a data signal, is retained by the retention capacitor. Accordingly, the driving current via the source and the drain of the first thin film transistor can flow for longer time than the period of supplying of the data signal.
(22) In the embodiment in which the retention capacitor is further provided, the arrangement may be such that the driving current compensation device controls a resistance between either of said first or second feeder lines and the retention capacitor, depending on a relationship between a voltage across the light-emitting device and the driving current.
According to the embodiment, a resistance between the first or the second feeder and the retention capacitor is controlled by the driving current compensation device depending upon a relationship between a voltage across the light-emitting device and a quantity of a driving current, thereby increasing the driving current to compensate for a reduction of the same driving current.
(23) In the embodiment employing the control of a resistance between a feeder line and the retention capacitor, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the driving current compensation device includes a third correction thin film transistor of the same channel type n or p as the first thin film transistor, having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the third correction thin film transistor of the same channel type n or p as the first thin film transistor, so that the driving current flowing from the first feeder line to the second feeder line is increased to compensate for the decrease of the same driving current.
(24) Alternatively, in the embodiment employing the control of a resistance between a feeder line and the retention capacitor, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the driving current compensation device includes a third correction thin film transistor of the same channel type n or p as the first thin film transistor, having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the third correction thin film transistor of the same channel type n or p as the first thin film transistor, so that the driving current flowing from the second feeder line to the third feeder line is increased to compensate for the decrease of the same driving current.
(25) Alternatively, in the embodiment employing the control of a resistance between a feeder line and the retention capacitor, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the driving current compensation device includes a fourth correction thin film transistor of the opposite channel type n or p to that of the first thin film transistor, having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the fourth correction thin film transistor of the opposite channel type n or p to the first thin film transistor, so that the driving current flowing from the first feeder line to the second feeder line is increased to compensate for the decrease of the same driving current.
(26) Alternatively, in the embodiment employing the control of a resistance between a feeder line and the retention capacitor, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the driving current compensation device includes a fourth correction thin film transistor of the opposite channel type n or p to that of the first thin film transistor, having a gate connected to an electrode on the first feeder line side of the light-emitting device and a source and a drain connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the fourth correction thin film transistor of the opposite channel type n or p to the first thin film transistor, so that the driving current flowing from the second feeder line to the first feeder line is increased to compensate for the decrease of the same driving current.
(27) In a different embodiment of the pixel circuit, the driving current compensation device controls a resistance between the first feeder and the second feeder, depending upon a relationship between a voltage across the light-emitting device and a quantity of the emitted light.
In this embodiment, a resistance between the first feeder and the second feeder is controlled by the driving current compensation device depending on a relationship between a voltage across the light emitting device and a quantity of the light emitted, whereby the driving current is increased in accordance with a decrease in a quantity of the light-emitting device.
(28) In the embodiment having the retention capacitor, the arrangement may be such that the driving current compensation device controls a resistance between either of the first or second feeder lines and the retention capacitor, depending on a relationship between a voltage across the light-emitting device and a quantity of the emitted light.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the driving current compensation device, whereby the driving current is increased in accordance with a decrease in a quantity of the emitted light.
(29) In the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending upon a relationship between a voltage and a quantity of emitted light, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the first thin film transistor is of a p channel type, while the driving current compensation device includes a first correction thin film photo-diode connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the first correction thin film photo-diode, whereby a driving current flowing from the first feeder line to the second feeder line through the p-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(30) In the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of emitted light, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the first thin film transistor is of a p channel type, and the driving current compensation device includes a fifth correction thin film transistor having a source and a drain connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the fifth correction thin film transistor, whereby a driving current flowing from the first feeder line to the second feeder line through the p-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(31) Alternatively, the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the first thin film transistor is of an n channel type, and the driving current compensation device includes a first correction thin film photo-diode connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the first correction thin film photo-diode, whereby a driving current flowing from the second feeder line to the first feeder line through the n-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(32) Alternatively, in the embodiment in which a resistance between the retention capacitor and the feeder line is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the first thin film transistor is of an n channel type, and the driving current compensation device includes a fifth correction thin film transistor having a source and a drain connected between the retention capacitor and the first feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the fifth correction thin film transistor, whereby a driving current flowing from the second feeder line to the first feeder line through the n-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(33) Alternatively, in the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the first thin film transistor is of an n channel type, and the driving current compensation device includes a second correction thin film photo-diode connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the second correction thin film photo-diode, whereby a driving current flowing from the first feeder line to the second feeder line through the n-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(34) Alternatively, in the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be higher than that of the second feeder line, and the first thin film transistor is of an n channel type, and the driving current compensation device includes a sixth correction thin film transistor having a source and a drain connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the sixth correction thin film transistor, whereby a driving current flowing from the first feeder line to the second feeder line through the n-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(35) Alternatively, in the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the first thin film transistor is of a p channel type, and the driving current compensation device includes a second correction thin film photo-diode connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the second correction thin film photo-diode, whereby a driving current flowing from the second feeder line to the first feeder line through the p-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(36) Alternatively, in the embodiment in which a resistance between the feeder line and the retention capacitor is controlled depending on a relationship between a voltage and a quantity of light emitted, the arrangement may be such that an electric potential of the first feeder line is set to be lower than that of the second feeder line, and the first thin film transistor is of a p channel type, and the driving current compensation device includes a sixth correction thin film transistor having a source and a drain connected between the retention capacitor and the second feeder line.
With this arrangement, a resistance between the first or second feeder line and the retention capacitor is controlled by the sixth correction thin film transistor, whereby a driving current flowing from the second feeder line to the first feeder line through the p-channel type first thin film transistor is increased in accordance with a decrease in a quantity of the emitted light.
(37) In a different embodiment of the pixel circuit, the driving current compensation device includes a thin film transistor which is formed in the same step of a process as the first thin film transistor.
This offers an advantage in that the production process does not necessitate any additional step for forming the current driving compensation device.
(38) In order to achieve the objects described before, a third display apparatus in accordance with the present invention comprises: a current driving type light-emitting device provided for each pixel; a driving device provided for each the pixel, for controlling a driving current flowing to the light-emitting device in accordance with a voltage of a data signal; a power source unit for supplying power source voltage through a power wire to cause the driving current to flow to the light-emitting device via the driving device; a signal line driving circuit for supplying, through a signal line, a data signal having a voltage corresponding to an image signal input from an image signal source to the driving device; a measuring unit for measuring at least one of a quantity of driving current flowing through the light-emitting device and a quantity of light emitted from the light-emitting device at the time when a data signal of a predetermined voltage is supplied to the driving device via the signal line; and a correction circuit provided between the image signal source and the signal line driving circuit, for inputting the image signal to the signal line driving circuit after correcting the image signal in such a manner that at least one of the measured quantity of driving current and the measured quantity of emitted light comes close to a predetermined reference value.
In the third display apparatus as defined above, a driving current flows to the light-emitting device via the driving device, as the power source voltage is supplied from the power source unit, while a data signal, which is received from the image signal source and which has a voltage corresponding to the image signal, is supplied to the driving device from the signal line driving circuit through the signal line. A driving current flowing to the light-emitting device is controlled by the driving device in accordance with a voltage of the data signal. As a consequence, the current driving type light-emitting device emits light by the driving current, in accordance with a voltage of the data signal. When a data signal of a predetermined voltage is supplied to the driving device through a signal line in, for example, a non-display period, the measuring unit measures a quantity of driving current flowing through the light emitting device or a quantity of light emitted from the same. Then, the correction circuit corrects the image signal in such a manner that the driving current or the light quantity as measured approaches a predetermined reference value( i.e., a reference voltage or a reference quantity). The corrected image signal is input to the signal line driving circuit. Consequently, the driving device is supplied with the data signal of a voltage corresponding to the corrected image signal, from the signal line driving circuit via a signal line.
Hence, even if a driving current or a light-emitting device is impeded as a result of deterioration over time of the light-emitting device or the driving device which causes an increase in a resistance of the light-emitting device or the driving device, a quantity of driving current or a quantity of light emitted in the corresponding light-emitting device is maintained substantially constant. Further, even if there are variations in current-voltage characteristics or current-light emitting characteristics of the light-emitting device or the driving device among a plurality of pixels, the quantity of driving current or the quantity of emitted light in the light-emitting device of the corresponding plurality of pixels can be substantially equalized, if the voltage control by the voltage adjusting unit is performed on independent pixels.
Thus, according to the third display apparatus, in a display apparatus in which the current driving type light-emitting device such as an organic EL device is driven by the driving device such as a thin film transistor, a decrease in screen luminance and screen irregularities caused by deterioration or variations in the characteristics can be reduced.
(39) In one form of the third display apparatus in accordance with the present invention, the driving device comprises a thin film transistor having a gate to be supplied with the data signal, and a source and a drain between which the driving current flows, a conductance between the source and the drain being controlled in accordance with the gate voltage.
With this arrangement, a conductance between the source and the drain of the thin film transistor is controlled in accordance with a voltage of the data signal supplied to the gate. It is therefore possible to control the driving current flowing through the light emitting device via the drain and the source can be controlled in accordance with the voltage of the data signal.
(40) Another form of the third display apparatus of the invention further comprises a memory device for storing at least one of the measured quantity of driving current and the measured quantity of emitted light, and the correction circuit corrects the image signal in accordance with at least one of the stored quantity of driving current and the stored quantity of emitted light.
With this arrangement, the current or light quantity as measured is stored in the memory device. The image signal is corrected by the correction circuit in accordance with the stored current or light quantity. It is therefore possible to perform the correction during the display period, based on the results of measurement conducted in a non-display period which precedes or follows the display period in point of time. It is also possible to perform correction on a plurality of pixels, using a common measuring unit and a correction circuit.
(41) In a further form of the third display apparatus of the present invention, the power source wire is provided for each pixel column, and the measuring unit measures a quantity of the driving current, the display apparatus further comprising a common line driving circuit which includes: a changeover switch for switching the power source wire to the power source unit side at a display period, and to the measuring unit side at a non-display period; a shift register for sequentially outputting sequential pulses in accordance with each power source wire; and a transmission switch for sequentially controlling conduction between each power source wire and the measuring unit in response to the sequential pulses at the non-display period.
According to this arrangement, during the display period, the change-over switch in the common line driving circuit connects the power source wire to the power source unit side, so that the light-emitting device is supplied with power source voltage from the power source unit to illuminate, thus performing ordinary displaying operation. On the other hand, in a non-display period, the power source wire is connected to the measuring unit side by the change-over switch. In the meantime, the shift register sequentially outputs sequential pulses, and the transmission switch operates in accordance with the sequential pulses so as to have conductance between each power source wire and the measuring unit, so that the measuring unit measures a quantity of driving current. Thus, the power source wires corresponding to the respective pixel columns are sequentially selected as the measuring object, whereby the driving currents for the successive columns of pixels are measured. Furthermore, measurement of the driving current can be conducted for each of the pixels, provided that a scanning signal is used to enable driving the light-emitting device on each pixel-line basis. It is therefore possible to perform correction on pixel-column basis or pixel basis.
(42) In a different form of the third display apparatus of the invention, the measuring unit measures a quantity of emitted light. This display apparatus further comprises: a light detecting line, provided for each the pixel column, for transmitting an electrical signal indicative of the quantity of emitted light to the measuring unit; and a light detecting line driving circuit which includes a shift register for sequentially outputting sequential pulses in accordance with each the light detecting lines, and a transmission switch for sequentially controlling conduction between each the light detecting line and the measuring unit in response to the sequential pulses at a non-display period.
In accordance with this arrangement, during a non-display period, the shift register sequentially outputs sequential pulses in accordance with the respective light detecting lines, and the transmission switch operates in response to the sequential pulses so as to have conductance between the successive light detecting lines and the measuring unit, so that the measuring unit measures a quantity of light emitted. Thus, the light detecting lines corresponding to the respective pixel columns are sequentially selected as the measuring object, whereby the quantities of emitted light are measured on pixel-column basis. Furthermore, measurement of the light quantity can be conducted for each of the pixels, provided that a scanning signal is used to enable driving the light-emitting device on pixel-line basis. It is therefore possible to perform correction on pixel-column basis or pixel basis.
(43) In a different form of the third display apparatus, the measuring unit measures the quantity of emitted light through measurement of a photo-excited current of a semiconductor device.
In accordance with this arrangement, a quantity of light emitted from the light-emitting device is measured by the measuring unit through measurement of the photo-excited current of the semiconductor element, and a correction is performed on the basis of the measured light quantity. It is therefore possible to perform measurement with a high degree of accuracy by using a comparatively simple device.
(44) When a quantity of light emitted is measured through measurement of photo-excitation current of the semiconductor device, the semiconductor device may be a PIN diode.
In this case, a quantity of light emitted from the light-emitting device can be measured by measuring the photo-excitation current at the PIN junction of the PIN diode.
(45) Alternatively, the semiconductor device may comprise a field effect transistor.
In this case, a quantity of light emitted from the light-emitting device can be measured by measuring the photo-excitation current at the channel of the field effect transistor.
(46) In a further alternative, the driving device comprises a thin film transistor which is formed in the same step of a process as the semiconductor device.
In this case, the driving device and the semiconductor element can be formed in the same step of a production process, which is advantageous from the production point of view.
(47) In a different form of the third display apparatus in accordance with the invention, the driving device comprises a polycrystalline thin film transistor formed through a low-temperature process of 600xc2x0 C. or less.
This feature makes it possible to form a driving device having high driving performance on a comparatively inexpensive large-size glass substrate or the like, thus contributing to a reduction in the production cost.
(48) In a different form of the third display apparatus, the light-emitting device comprises an organic electroluminescent device formed through an ink-jet process.
This feature enables production of a light-emitting device having high illuminating efficiency and capable of standing a long use, contributing to easy patterning on the substrate. Further, the production process can be implemented by using a comparatively inexpensive apparatus, while reducing the amount of material to be wasted from the process, contributing to a cost reduction in the display apparatus.
(49) In a different form of the third display apparatus, the measuring unit measures at least one of the driving current and the quantity of emitted light for each pixel, and the correcting circuit corrects the image signal for each pixel.
In accordance with this arrangement, the measurement of the driving current or the quantity of emitted light is performed by the measuring unit on a pixel basis, and the correction of the image signal by the correction circuit also is conducted on a pixel basis. It is therefore possible to substantially equalize a quantity of driving current or a quantity of emitted light of the light-emitting device in the corresponding plurality of pixels, despite any variation among the pixels in regard to voltage-current characteristics and current-light-emitting characteristics of the light-emitting device and the driving device, attributable to variations incurred during the production and variations of degree of deterioration. It is thus possible to reduce any screen irregularities, attributable to variations in the characteristics of each device.
(50) In a different form of the third display apparatus, the measuring unit measures at least one of the driving current and the quantity of emitted light for each predetermined block having a number of pixels, and the correcting circuit corrects the image signal for the each predetermined block.
According to this arrangement, the measurement of the driving current or the emitted light quantity is performed by the measuring unit on a predetermined pixel-block basis, each block having a number of pixels. In addition, the correction of the image signal is performed by the correction circuit on the predetermined pixel-block basis. For instance, one pixel block includes n pieces of adjacent pixels (n being 2, 4, 8, 16. 32. 64 or so). The number of pixels contained in the pixel block may be determined based on factors such as the required level of uniformity of luminance, processing performance of the measuring unit and the correction circuit, and so forth. It is therefore possible to substantially equalize a quantity of driving current and a quantity of emitted light among a plurality of pixel blocks, despite any variation among the pixel blocks in regard to voltage-current characteristics and current-light-emitting characteristics of the light-emitting device and the driving device, attributable to variations incurred during the production and variations of degree of deterioration. It is thus possible to reduce any screen irregularities, attributable to variations in the characteristics of each device. In this case, the measurement and correction can be performed more easily in shorter time, as compared with the case where the measurement and the correction are performed on a pixel basis.
(51) In a different form of the third display apparatus, the correcting circuit corrects the image signal by converting a signal level of the image signal from a specified signal level to another specified signal level.
In accordance with this form of the display apparatus, the correction of the image signal by the correction circuit is performed such that the signal level of the image signal is converted from a specified signal level to another specified signal level. This eliminates the necessity of provision of signal levels different from the specified signal levels, thus offering advantages such as simplification of the signal line driving circuit or reduction in the number of power sources required for the signal line driving circuit. Consequently, the display apparatus can operate at high speed with reduced electrical current, using a simplified circuitry.
(52) In order to achieve the above-described object, a fourth display apparatus of the present invention incorporates any of the foregoing pixel circuits, for each of the pixels.
In the fourth display apparatus as defined above, since each pixel is driven and controlled by its own pixel circuit of the present invention, it is possible to reduce screen irregularities and reduction in the display luminance which are attributable to deterioration over time and variations in characteristics of the light-emitting device and the driving device, thus achieving a high quality of image display.
(53) In order to achieve the object of the invention described before, an electronic apparatus of the present invention incorporates any form of any one of the first to third display apparatuses of the invention.
By virtue of the use of the display apparatuses of the invention, reduction in the display luminance and screen irregularities attributable to deterioration over time and variations in characteristics of the light-emitting device and the driving device, can be suppressed. It is thus possible to obtain a variety of types of electronic apparatuses capable of providing high quality of image display.